The present invention generally relates to a floppy disk drive controller for interfacing a microprocessor system with a floppy disk drive. The present invention more particularly relates to such a floppy disk drive controller having an improved density select for use with a floppy disk drive of the type capable of receiving data bits having at least three different data rates, for providing the floppy disk drive with rate control signals to condition the floppy disk drive to receive the data bits from the floppy disk drive controller at one of the at least three different data rates. The floppy disk drive controller of the present invention is also compatible with floppy disk drives capable of receiving data bits at two different rates and further includes a rate controller for receiving data rate control signals directly from the microprocessor to provide data rate control redundancy.
Computer systems generally employ a microprocessor having internal and/or external memory. To interface the microprocessor system to a floppy disk drive, such systems also generally include a floppy disk drive controller. Such controllers are utilized to convert parallel-bits of data from the microprocessor system to serial-bits of data and to provide the floppy disk drive with the serial-bits of data. Along with the serial-bits of data, the floppy disk drive controllers provide the floppy disk drives with various control signals, well known in the art, including density select or data rate control signals to condition the floppy disk drives to receive the serial-bits of data from the floppy disk drive controllers at a rate dictated by the microprocessors.
Floppy disk drives which have been commonly used in the past have been capable of receiving the data bits at two different rates, five hundred kilobits per second (500 Kbps) and two hundred and fifty kilobits per second (250 Kbps) or three hundred Kilobits per second (300 Kbps). Floppy disk drive controllers used in conjunction with such floppy disk drives have provided a single rate control signal, commonly referred to in the art as a density select signal (DENSEL), having one of two levels responsive to commands from the microprocessor for conditioning the floppy disk drives to receive the data bits at one of these two different rates. A high level of the single data rate control signal has conditioned the floppy disk drives to receive the microprocessor data bits at the 500 Kbps rate and a low level of the single data rate control signal has conditioned the floppy disk drives to receive the microprocessor data bits at the 250 Kbps or 300 Kbps rate.
Improved floppy disk drives known as extended floppy disk drives are not only arranged to receive microprocessor data bits at the 500 Kbps and 250 Kbps or 300 Kbps rates, but also at a one megabit rate (1 Mbps). Unfortunately, floppy disk drive controllers have not been able to accommodate these improved floppy disk drives because they have not provided the necessary data rate control signals to activate the 1 Mbps rate of such floppy disk drives.
The floppy disk drive controller of the present invention overcomes this deficiency in prior art floppy disk drive controllers by providing the necessary rate control signals for conditioning the improved floppy disk drives to receive microprocessor data bits at any one of the three data rates of 300 Kbps or 250 Kbps, 500 Kbps, and 1 Mbps. In addition, as will be seen hereinafter, the floppy disk drive controller of the present invention is also capable of providing a single data rate control signal for conditioning the first mentioned floppy disk drives to receive microprocessor data bits at either the 250 or 300 Kbps or 500 Kbps data rates so as to be compatible therewith. The floppy disk drive controller of the present invention also includes a separate data rate control adapted to receive data rate control signals directly from the microprocessor to provide system data rate control redundancy.